The present invention pertains generally to catheters and methods for the manufacture of catheters. More particularly, the present invention pertains to multi-lumen catheters that are made from a plurality of individual tubes. The present invention pertains particularly, though not exclusively, to multi-lumen catheters having low profiles.
There are numerous health care situations wherein a multi-lumen catheter is useful in the treatment of a patient. For instance, it may be necessary for a patient to receive several different medications at the same time. A multi-lumen catheter can simultaneously infuse a plurality of medications into a patient and, if necessary or desirable, the separate lumens of the multi-lumen catheter can prevent the medications from interacting with each other during the infusion process into the patient. Another example where a multi-lumen catheter may be useful is when it is necessary to infuse medication into a patient""s body while simultaneously withdrawing bodily fluid samples such as blood from the patient.
For several reasons, whenever interventional procedures are required, it is most often desirable to perform the necessary treatment on the patient through a single puncture site. The use of a multi-lumen catheter obviously eliminates the need for numerous punctures in a patient and thus minimizes patient discomfort.
Several types of multi-lumen catheters are well known. For example, U.S. Pat. No. 5,167,623 which issued to Cianci, et al. for an invention entitled xe2x80x9cMultilumen Catheterxe2x80x9d discloses a multi-lumen catheter having a flexible first tube and a flexible dual-lumen tube which is disposed in the first tube. Another example of a multi-lumen catheter is U.S. Pat. No. 4,072,146 which issued to Howes for an invention entitled xe2x80x9cVenous Catheter Device.xe2x80x9d This patent discloses three independent non-coaxial circular tubes placed in a larger tube. Yet another example is a multi-lumen catheter having a unitary catheter tube with a septum forming two large, roughly elliptically shaped lumens and a small infusion lumen extending along the interior wall of the unitary tube. Such a multi-lumen catheter is disclosed in U.S. Pat. No. 5,221,256 which issued to Mahurkar for an invention entitled xe2x80x9cMultiple-Lumen Catheter.xe2x80x9d
Despite the fact there are many multi-lumen catheters in the pertinent art, there still exist several common problems associated with these types of catheters. For example, a typical problem concerning a multi-lumen catheter is its size. In order to minimize trauma to the patient, however, it is desirable to make the smallest possible puncture in a patient""s body. Consequently, a catheter should have the smallest possible cross-sectional area. Some multilumen catheters, however, use additional material to hold the plurality of tubes together which can really increase the cross-sectional area. An example of this is the multi-lumen catheter mentioned above which is disclosed in U.S. Pat. No. 4,072,146 having three independent non-coaxial tubes disposed in a larger tube. The cross-sectional area of this particular multi-lumen catheter is relatively large because of the additional large tube that is used to hold the three tubes together.
In addition to problems with large cross-section areas, multi-lumen catheters can also have problems regarding steerability and pushability. For instance, a catheter must be flexible in order for the catheter to be steered and maneuvered through the convoluted and narrow passageways of the body. At the same time, however, the catheter must also be sufficiently stiff for the catheter to be pushed into the passageway to reach a site that is at a considerable distance from the point of entry of the catheter into the patient""s body. The problems with steerability and pushability derive from the material with which the multi-lumen catheter is made. The crux of the problem is that a material usually possesses one good characteristic at the expense of other characteristics. Therefore, multi-lumen catheters that are made of only one material may not sufficiently accomplish all the functional requirements.
In light of the above, it is an object of the present invention to provide a multi-lumen catheter having a low profile and a method for manufacturing such a catheter. Another object of the present invention is to provide a multilumen catheter having a plurality of independent catheter tubes that are fused together to reduce their cross-sectional profile. Yet another object of the present invention is to provide a multi-lumen catheter having catheter tubes that can be made from different thermoplastic materials and having varying lengths to provide for operational requirements. Still another object of the present invention is to provide a multi-lumen catheter which is relatively simple to manufacture, easy to use, and comparatively cost effective.
The present invention is directed to a multi-lumen catheter and a method for manufacturing such a catheter. For the present invention, the multi-lumen catheter includes a plurality of individual catheter tubes, each having an outer surface, an inner surface, and a lumen. As intended for the present invention, the plurality of catheter tubes may have varying lengths as well as varying diameters. Importantly, each catheter tube can be made of a selected thermoplastic material, and the various tubes can be made of different materials. Of equal importance, the catheter tubes can also be made of the same thermoplastic material, if so desired.
In the manufacture of the present invention, a mandrel is first inserted into the lumen of each catheter tube to provide support to the catheter tubes. Next, the plurality of catheter tubes are juxtaposed with each other in a coextended desired arrangement. It is important for the outer surface of one catheter tube to be in contact with the outer surface of at least one other catheter tube in the arrangement. The arrangement of the catheter tubes is then disposed in a sleeve which holds the catheter tubes in place and prevents them from crossing or tangling with each other.
In fusing the catheter tubes to each other, the arrangement of catheter tubes is first placed in front of a heating cylinder. The plurality of catheter tubes in the sleeve are then simultaneously advanced through the sleeve, and through the heating cylinder. As the catheter tubes are advanced through the heating cylinder, the outer surfaces of the catheter tubes are fused together where their outer surfaces are in contact with each other. As a result, there is a change in structure as the outer surfaces of the individual catheter tubes become a contiguous outer surface for the fused catheter tubes.
In any case, the sleeve continues to hold the remaining lengths of the catheter tubes in place as they are advanced into the heating cylinder. The sleeve itself, however, does not enter the heating cylinder. In this manner, the plurality of catheter tubes of the present invention continue to be advanced through the heating cylinder until the entire lengths of the catheter tubes are fused.
As stated above, each catheter tube can be made of a different thermoplastic material. It is necessary, however, for each thermoplastic material to be miscible with each other. Stated another way, the melting point temperatures of the thermoplastic materials are in a close range of each other. This is important because the outer surface of each catheter tube must melt as it is advanced through the heating cylinder.
It is important to note that the method of the present invention for fusing the catheter tubes together is dependent upon the temperature that is used for fusing, the time the materials are exposed to the heat and the volume and surface contact area of the materials that are being fused. Insofar as temperature is concerned, the heating cylinder is operated at a substantially constant temperature that is greater than the lowest melting point temperature of the thermoplastic materials that are being used for the catheter tubes. Further, the rate at which the catheter tubes pass through the heating cylinder will vary depending upon the size of the catheter tubes and the number of catheter tubes that are to be fused together. For example, the rate at which two catheter tubes pass through the heating cylinder will most likely be faster than the rate for three catheter tubes because two catheter tubes will fuse faster than three catheter tubes. In any case, the purpose here is to have the outer surfaces of the catheter tubes melt uniformly as the heating cylinder radiates heat on the arrangement of the catheter tubes.
Importantly, only the outer surfaces of the catheter tubes are melted during the manufacture of a multi-lumen catheter. Unlike the outer surfaces of the catheter tubes that are heated and fused to each other, the temperature of the material at the inner surfaces of the catheter tubes needs to be held below the melting point in order to maintain the structural integrity of the catheter tubes. In order to prevent the inner surfaces of the catheter tubes from melting, the inside surface of each catheter tube needs to be cooled. This can be done by the mandrel, which generally acts as a sufficient heat sink. Alternatively, air or water can be blown through each mandrel in each catheter tube to prevent the inner surface of the catheter tube from melting. For the present invention, the mandrel is preferably a stainless steel hypo tube.
As also contemplated in the manufacture of the multi-lumen catheter of the present invention, in order to properly perform a specific function, a catheter tube can include an inner liner which may be of a material that is suitable for the purpose. For example, a particular liner may be preferred for infiltrating radiopharmaceuticals through the catheter tube. In this case, the inner liner is preferably made of polyethylene. The catheter tube itself, however, may be immiscible with its liner. For example, when the tube is made of polybutylene terephthalate polyether glycol, which is sold under the trademark HYTREL(copyright), the polyethylene inner liner of the catheter tube may not fuse with the polybutylene terephthalate polyether glycol material of the other catheter tube. In this case, a tie layer may need to be used to bond the inner liner with the thermoplastic material of the catheter tube. A tie layer suitable for this example is preferably made of a polyolefin adhesive, such as the material sold under the trademark PLEXAR PX380(copyright).